1. Field of the Invention
The present invention relates to a dosing device for the volumetric dosing of a liquid additive which is added in a certain volume ratio to a fluid flowing in a first hose line via a second hose line which feeds directly or indirectly into the first hose line. The dosing device of the present invention includes a hose or tube section, which is called a drip tube, which extends downstream from the junction, and has a drip chamber connecting downstream from the drip tube and a light barrier. The direction of action of the light barrier is arranged transversely to the fall path of the drops. Such a dosing device is used in particular within a system for the collection and retransfusion of autologous blood in order to add an anticoagulant liquid or a sedimentation accelerator to blood drawn, or sucked-off and intended for retransfusion, for example during an operation or similar.
2. Discussion of Background and/or Material Information
A system for the collection and retransfusion of autologous blood is, for example, known from EP-OS 0 483 703. In the known system, a collection vessel is subjected to an underpressure which is used, by means of a hose attached to the collecting vessel, to suck off blood from an operative field, i.e. from the body of a patient. The sucked-off blood, which is called drainage blood, flows through the hose line and passes a quantity dosing device before it drips into the collection container. Arranged upstream of the quantity dosing device is a Y-shaped branching or junction into which a second hose feeds which is connected to a reservoir for an anticoagulant liquid and/or a sedimentation accelerator. Situated between the reservoir for the anticoagulant liquid and the Y-shaped branching is a valve means which can be triggered via the previously mentioned quantity dosing device.
Conventional dosing devices, known from the prior art, operate according to the principle of drop counting, whereby the fluid which flows in a tube and is to be measured or monitored, is guided to a drip chamber which is surrounded by a light barrier. A drop of liquid falling in the drip chamber breaks the light beam from the light barrier and so generates a counting pulse which can be fed to a microprocessor or similar means for further evaluation. It is a disadvantage with this type of volume measurement of a flowing liquid that, the greater the viscosity fluctuations experienced by the liquid to be measured, the more inaccurate is the measured result. The reason for this is that changing kinematic tenacity, i.e. viscosity, and changing density bring with them a change in the volume of an individual drop. As it is only the absolute number of fallen drops which can be determined by the light barrier, this leads the actual volumetric mixture ratio to change when a certain volume of additive is added to a certain number of fallen drops, for example, by a signal being generated by the quantity dosing device after a certain number of fallen drops, ascertained by means of the light barrier, by means of which the valve means arranged in the hose line and connected to the reservoir of the anticoagulant liquid is triggered and opened for a certain time interval.
On the other hand, the principle of volume determination by means of a drip chamber and light barrier is cheap and easy to put into practice and operates, at least as far as the light barrier component is concerned, without contact, which, in particular in the case of systems and devices which process blood of patients, is highly desirable for reasons of hygiene.